Substrate-based integrated circuit (IC) packages include BGA packages, BGA standing for Ball Grid Array. In U.S. Pat. No. 6,048,755 A, a method for producing a BGA package by using a substrate with a patterned solder resist mask is described. In this arrangement, a number of IC packages can be arranged on a common substrate strip (matrix strip).
In such substrate-based IC packages, the mold cap (covering material or mold compound) is used to protect the chip edges since cracks or other mechanical damage can also affect the active chip side. Such damage can be produced during the handling, during the back-end process and also at the customer. The mold cap encloses the back of the chip and adjoining areas of the substrate.
In these IC packages, the chip can be fixed on the substrate in different ways. Thus, the chips are mounted, for example, by means of a tape or a printed or dispensed adhesive. It is particularly effective to print the adhesive onto the substrate by interposing a printing template and then to bond the chip to the substrate. To ensure a reliable adhesive printing process in this case, particularly on matrix substrates, the solder resist is omitted in the package area on the chip side. This additionally impedes contamination and a sufficient support area is created for the printing template used during the printing process. Matrix substrates are understood to be substrates, which are provided for accommodating a multiplicity of chips.
The adhesive has been previously printed with the aid of a squeegee and a printing template onto substrates, which were covered with solder resist over the whole area or at least most of the area on the chip side. However, this results in the risk, particularly in substrates with a bond channel, that during the die attach process (chip assembly process) contamination of the wire bond area on the chip can occur due to flowing of the adhesive. The adhesive can flow over the edge of the bond channel to the vicinity of the bond pad on the chip, which would have extremely negative effects for the wire bond process.
The applied adhesive was thus an additional layer on the solder resist. If then the solder resist is left off at least partially in the package area on the chip side, there is no support area (spacer) for the printing template, particularly in the case of matrix strips, and a cover with solder resist is necessary for process reasons (e.g., substrate warpage, mold sealing ring) on the substrate edge around the chip area. As a result, however, support area is lacking in the center of the matrix, which results in non-uniform bending of the printing template in the direction of the area to be printed. This also has the effect that the applied adhesive has a non-uniform thickness.